1. Field of the Invention
The present invention relates to a method of detecting leakage in a system for absorbing evaporated fuel from a fuel tank and for purging the absorbed fuel into an intake pipe of an internal combustion engine mounted on an automobile. The detection of the leakage is performed after the engine is stopped.
2. Description of Related Art
An evaporated fuel control system, in which fuel evaporated from a fuel tank is absorbed to an absorbing material such as grain-shaped activated carbon, and the absorbed fuel is purged into an intake pipe of an engine by a negative pressure developed in the intake pipe, is known hitherto. In order to prevent fuel leakage from the system, it is necessary to detect pressure leakage in the system. In detecting the leakage, the system is closed from the atmospheric pressure. Then, an inner space of the system is pressurized by a pump, and a pressure therein is measured to detect the pressure leakage. Alternatively, the leakage is detected, without pressurizing the inner space, by comparing a measured pressure in the closed space with a predetermined pressure corresponding to an ambient temperature or a temperature in the inner space measured at that time.
In any case, communication between the system and the atmospheric pressure has to be shut-off to measure the inner pressure for detecting the pressure leakage. The communication with the atmospheric pressure is shut-off by turning on an electromagnetic valve disposed in the system. After the leakage detection is completed, the electromagnetic valve is turned off to establish again the is communication between the system and the atmospheric pressure. Since the leakage detection is performed while the engine is not operating, an on-board battery cannot be charged by a generator driven by the engine, and electric power for energizing the electromagnetic valve has to be supplied solely from the on-board battery. In addition, the electromagnetic valve has to be kept energized for a certain period of time until the pressure and temperature in the system is stabilized. Accordingly, the battery power is consumed in the process of detecting the pressure leakage.